The extremely nonlinear interaction between waves and marine structures is one of most challenging problems in ocean engineering. In this study, the propagation of a solitary wave over a submerged vertical obstacle is investigated by a developed two-dimensional multi-phase viscous model. The constrained interpolation profile (CIP) based on Cartesian grid method is introduced to solve the Navier-Stokes equations, and free surface is captured accurately by the Tangent of Hyperbola for INterface Capturing (THINC) scheme. First, the free surface motions and velocity fields of a solitary wave interacting with a submerged obstacle are simulated. The present calculations fit fairly well with the measurements through whole wave propagation over the submerged obstacle. Second, the corresponding vorticity fields are calculated to illustrate characteristics of vortex generation and evolution. Third, wave forces acting on the submerged obstacle are calculated, and the results agree
well with existing computations. Finally, the effectiveness of the submerged obstacle as a targeted breakwater is estimated by evaluating the reflection and transmission coefficients. The presented computations confirm that the CIP-based Cartesian grid method is capable of
reproducing strongly nonlinear interaction of a solitary wave with the submerged obstacle and performing predictions of comprehensive flow-field information accurately.